This invention relates generally to an electrostatographic copier or printer, and more particularly, concerns a cleaning apparatus using uniform air velocity. In an electrophotographic application such as xerography, a charge retentive surface (i.e., photoconductor, photoreceptor or imaging surface) is electrostatically charged, and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charge surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly.
Although a preponderance of the toner forming the image is transferred to the paper during transfer, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom.
A commercially successful mode of cleaning employed on automatic xerographic devices utilizes a brush with soft conductive fiber bristles or with insulative soft bristles which have suitable triboelectric characteristics. While the bristles are soft for the insulative brush, they provide sufficient mechanical force to dislodge residual toner particles from the charge retentive surface. In the case of the conductive brush, the brush is usually electrically biased to provide an electrostatic force for toner detachment from the charge retentive surface. Toner particles adhere to the fibers (i.e. bristles) of the brush after the charge retentive surface has been cleaned. The process of removing toner from these types of cleaner brushes can be accomplished in many ways. Typically, brush cleaners, use flicker bars to provide the detoning function.
Problems that can be associated with flicker bar detoning include damage to the cleaner brush as a result of the high impact forces at the point of contact, resulting in shorter brush lives and, higher cleaner unit manufacturing cost (UMC) due to periodic replacement or cleaning of the flicker bars.
Typically, rotary brush cleaners also encounter problems with photoreceptor filming and abrasion, and toner emissions. The filming and abrasion are due to the high impact forces that result when the brush fibers strike the toner and photoreceptor. Toner emissions usually result from inadequate or non-uniform air flow entering the cleaner at the housing to photoreceptor gaps.
High velocity air streams have been used to clean photoreceptors in the past. Photoreceptors and BTRs, have used air knives to create a high velocity air stream to clean their surfaces. Such devices can consist of a plate, closely spaced to the surface to be cleaned, with narrow slots cut into it. A vacuum is applied behind the plate to cause air to flow through the slots and create a high velocity airstream across the surface being cleaned. The high velocity air flow disturbs the surface boundary layer allowing removal of particles adhered to the surface. The problems with this approach are in the manufacture of the device and the power required to create the vacuum. The tolerances for the cleaner and the surface to be cleaned must be held closely. The orifice slot width must be uniform along its length to maintain uniform air velocities and therefore cleaning. The spacing between the plate and surface to be cleaned must also be uniform for the same reasons. This requires the plate and cleaning surface to be straight, flat and well aligned. If the surface to be cleaned is a roll, the runout of the roll and the parallelism of the roll axis to the slot axis is also important. Because of the close spacing of the cleaning plate to the surface to be cleaned and the narrow orifice slot, the resistance of the system to air flow is very high. As a result of this high resistance to air flow, a considerable air flow is required to generate the required cleaning air velocities needed for the narrow orifice slot to clean the surface. The requirements of high pressure and air flow result in a high power usage for the system and the possibility of a noise problem.
In practice, toner often times is not completely removed from the chamber of the cleaning apparatus due to uneven air flow over the length of the brush and within the chamber. This uneven air flow causes nonuniform cleaning of the rotating brush and results in deposition of the toner in areas of the chamber where the air flow velocity becomes too low to transport toner. Eventually, air flow and cleaning efficiency can be reduced to a point where residual toner material is left on the photoconductive member and is transferred to subsequent receiver sheets resulting in copies with ghost images or high density background.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 4,459,012 to Allen et al. discloses a cleaning apparatus having a manifold housing which partially encloses a rotating brush. A chamber, defined by the manifold housing, has a plurality of air flow dividers disposed therein forming channels extending from a position spaced near the brush into an outlet port which is coupled to a vacuum source. These channels direct air flow across the cleaner brush to remove toner therefrom.
U.S. Pat. No. 4,809,035 to Allen, Jr. discloses an apparatus for separating and removing non-magnetic lubricating particles. An air manifold assembly, having a blower, is mounted on the toner unit housing, of the unwanted particle chamber, to draw the unwanted particles from such chamber.
U.S. Pat. No. 3,793,986 to Latone discloses a toner powder reclaiming system for use in conjunction with a photoreceptor cleaning device. The system includes a particle separator in the path of movement of air flow containing toner particles from a brush cleaning device. The toner particles are separated from cleaning debris particles and conveyed to a collection manifold and thence to collecting containers.